1. Field of the Invention
The present invention relates to a heat exchanger configured of a plurality of first and second plate members stacked alternately and brazed, each forming a three-layer clad aluminum-alloy structure, or in particular to a brazed structure of a housingless type oil cooler capable of preventing the corrosion of the wall of the path of the cooling water constituting a cooling medium for an oil.
2. Description of the Related Art
In a conventional housingless type oil cooler 100, as shown in FIGS. 12 and 13, a plurality of dish-shaped plates 101 having substantially the same contour are stacked and integrally brazed to each other along the arranged on the lower end of a plate stack-type core portion 102 including a plurality of the stacked plates 101. A flat cooling water path 104 is formed between some adjacent ones of the plates 101. A flat oil path 105 is formed between other adjacent ones of the plates 101. These paired structures are alternated in the direction along the thickness of the plates 101. A cooling water inlet pipe 106 and a cooling water outlet pipe 107 are mounted on the uppermost plate 101, and a packing 108 is mounted on the seat member 103. Heat transmission fins 109 are arranged in each of the oil paths 105.
Each of a plurality of the plates 101 used for this housingless oil cooler 100, as shown in FIG. 14, is an aluminum-alloy three-layer clad structure (three-layer structured plate member) formed of an aluminum-alloy core member 110 which is clad, on the two sides thereof, with first and second brazing material layers 111, 112 of an aluminum alloy such as Alxe2x80x94Si. The flat portions of a plurality of the plates 101 are each constructed in such a manner that the first brazing material layer 111 and the second brazing material layer 112 is arranged in opposed relation to each other with the cooling water path 104 or, as the case may be, the oil path 105 therebetween. Also, the outer peripheral portion of each of the plates 101 which is located outside of the flat portion thereof is bent so that the surfaces of the first brazing material layer 111 of a given plate 101 and the second brazing material layer 112 of an adjacent plate 101 are in contact with each other.
The conventional housingless type oil cooler 100, however, poses the problem that once the cooling water providing an oil cooling medium is degenerated and becomes corrosive, that wall of the aluminum-alloy plates 101 which is nearer to the cooling water path is easily corroded and the service life of the cooler is shortened. As a solution to this problem, an aluminum-alloy three-layer clad structure (three-layer structured plate member) has been conceived in which an aluminum-alloy sacrificing material layer is clad on that side surface of the aluminum alloy core member constituting each plate 101 which is nearer to the cooling water path and an aluminum-alloy brazing material layer is clad on the side surface of the core member nearer to the oil path. This poses another problem, however, that for lack of a brazing material in the joint between the peripheral portions of adjacent plates 101, the peripheral portions of adjacent plates 101 cannot be brazed to each other.
As a method to solve this problem, a housingless type oil cooler (Japanese Unexamined Patent Publication No. 10-185462) of an aluminum-alloy four-layer clad structure (four-layer structured plate member) has been proposed, in which as shown in FIG. 15, a first aluminum-alloy sacrificing material layer 121 is clad on one side surface of the aluminum-alloy core member 120 of the plate 101, while a second aluminum-alloy sacrificing member 122 is clad on the other side surface of the core member 120, and the surface of the second sacrificing member 122 is clad with an aluminum-alloy brazing material layer 123. The outer peripheral portion of each of these plates 101 is bent in such a manner that the surface of the brazing material layer 123 is in contact with the surface of the first sacrificing material layer 121 of an adjacent plate 101. With this structure, the presence of the brazing material in the joint of the outer peripheral portion of each plate 101 improves the coupling strength and the sealability of the joint of the outer peripheral portion of each plate 101. Nevertheless, the use of a four-layer structure for the plate 101 poses the problem of a higher material cost and the resulting higher product cost.
A three-layer structured plate member with a Zn-contained brazing material layer doubling as a sacrificing member clad on the two side surfaces of the aluminum-alloy core member may be considered as still another solution. When integrally brazing this structure in a heating furnace, however, the Zn component is liable to be evaporated on the one hand and the brazing material layer is concentrated at the joint by surface tension on the other hand. Thus, the amount of the sacrificing material is difficult to control, and the resulting insufficient corrosion resistance is liable to lead to the corrosion of the wall surface of the plate member nearer to the cooling water path.
The object of the present invention is to provide a low-cost heat exchanger of aluminum comprising first and second three-layer structured plate members as first and second plates, respectively. Another object of the invention is to provide a heat exchanger of aluminum in which the coupling strength and the sealability of the joint of the peripheral portions of the first and second plate members can be improved while at the same time maintaining the corrosion resistance of the first and second plate members.
According to one aspect of the invention, there is provided a heat exchanger of aluminum comprising:
a plurality of first plates each constituting a three-layer structured first plate member including a first aluminum-alloy core member, a first sacrificing material layer clad on one side surface of the first core member and a first brazing material layer clad on the other side surface of the first core member; and
a plurality of second plates each constituting a three-layer structured second plate member including a second aluminum-alloy core member, a second brazing material layer clad on one side surface of the second core member and a second sacrificing material layer clad on the other side surface of the second core member. As a result, the material cost of the heat exchanger of aluminum can be reduced for a lower product cost.
A plurality of the first plate members and the second plate members are arranged alternately in the direction along the thickness thereof in such a manner that the first sacrificing material layer and the second sacrificing material layer are in opposed relation to each other with a first fluid path therebetween while the first brazing material layer and the second brazing material layer are in opposed relation to each other with a second fluid path therebetween. This assembly is heated to higher than the melting points of the first and second brazing material layers in a heating furnace or the like. In this way, each joint between the first and second plates can be positively brazed to couple them to each other while holding the first and second sacrificing material layers on the side of each of the first and second plates exposed to the corrosive environment.
The outer peripheral edge portion of each first plate member is deformed in such a manner that at least the first brazing material layer is interposed in the joint between the outer peripheral portion of the first plate member and the second plate member or the first plate member. This assembly is heated to higher than the melting points of the first and second brazing material layers in a heating furnace or the like. As a result, the joint between the outer peripheral portion of the first plate member and the second plate member or the first plate member can be positively brazed and coupled to each other while holding the first and second sacrificing material layers on the side of each of the first and second plates exposed to the corrosive environment.
Further, the first plate member has a flat defining portion for defining the first fluid path and the second fluid path. Also, the outer peripheral portion of the first plate member includes a vertical wall portion bent in the direction along the thickness orthogonal to the direction along the surface of the defining portion from the outer peripheral end of the defining portion, and an outer peripheral edge portion bent in the direction along the surface of the defining portion from the forward end of the vertical wall portion. The outer peripheral edge portion is arranged in such a manner that the surface thereof is in contact with the surface of the second plate member through the first brazing material layer. In this way, the surfaces of the outer peripheral portion of the first plate member and the second plate member or the first plate member can be brazed to each other thereby minimizing the insufficiently brazed portions.
According to another aspect of the invention, there is provided a heat exchanger of aluminum, wherein the outer peripheral portion of each of the first plate members is deformed to have a section in the substantial shape of a U, V or C. As a result, even in the case where the first and second plate members are alternately stacked in the direction along the thickness thereof in such a manner that the first sacrificing material layer and the second sacrificing material layer are in opposed relation to each other with the first fluid path therebetween, the joint between the outer peripheral portion of the first plate member and the second plate member or the first plate member can be positively brazed.
According to still another aspect of the invention, there is provided a heat exchanger of aluminum, wherein the second plate member is bent to have a stepped surface. The outer peripheral portion of the second plate member is bent to have a section in the substantial shape of L, and between the extension portion and the outer peripheral edge portion of the second plate member, a second bent portion is formed for engaging the first bent portion between the defining portion and the vertical wall portion of the first plate member. As a result, the first plate member and the second plate member can be readily set in position with each other.
According to yet another aspect of the invention, there is provided a heat exchanger of aluminum, wherein a first fluid path through which a corrosive fluid (first fluid) flows is formed between the second sacrificing material layer side surface of the second plate member and the first sacrificing material layer side surface of the first plate member. Also, a second fluid path through which a non-corrosive fluid (second fluid) flows is formed between the first brazing material layer side surface of the first plate member and the second brazing material layer side surface of the second plate member. The wall of the first fluid path is exposed to a more corrosive environment than the wall of the second fluid path.
According to a further aspect of the invention, there is provided a heat exchanger of aluminum, which is preferably a housingless type heat exchanger with at least a part of the outer peripheral portion of the first plate member forming an outer wall portion.
The present invention may be more fully understood from the description of the preferred embodiments of the invention set forth below together with the accompanying drawings.